Near Field Communication (NFC), enables data to be exchanged between devices over short distances of up to about 10 cm or so. NFC is essentially an extension of Radio Frequency IDentification (RFID) technology which integrates a smartcard and reader into a single device. Consequently, NFC is compatible with contactless infrastructure as used for payment on public transport systems for example.
NFC technology is particularly suited for transferring data to and from cellular telephones fitted with NFC readers. Apart from its compatibility with existing RFID devices, NFC has a number of advantages over Bluetooth technology and the like. Notably, NFC does not require manual configurations of the communicating devices and so has a much shorter set-up time than other technologies.
A further feature of NFC is that an NFC reader may behave as a transponder with the NFC antenna drawing energy from the incoming electromagnetic signal by electromagnetic induction. Thus, for example, data may be transferred to an NFC-enabled mobile phone, even when the phone is switched off.
Electromagnetic induction allows energy to be transferred from a power supply to an electric load without requiring a conduction path therebetween. A power supply is wired to a primary coil and an oscillating electric potential is applied across the primary coil, thereby inducing an oscillating magnetic field. The oscillating magnetic field induces an oscillating electrical current in a secondary coil placed within this field. Thus, electrical energy may be transmitted from the primary coil to the secondary coil by electromagnetic induction, without the two coils being conductively connected. When electrical energy is transferred from a primary coil to a secondary coil in this manner, the pair are said to be inductively coupled. An electric load wired in series with such a secondary coil may draw energy from the power source when the secondary coil is inductively coupled to the primary coil.
Inductive battery charger systems are known, such as the system described in U.S. Pat. No. 7,164,255 to Hui, which is incorporated herein by reference. In Hui's system a planar inductive battery charging system is designed to enable electronic devices to be recharged. The system includes a planar charging module having a charging surface on which a device to be recharged is placed. Within the charging module and parallel to the charging surface, is at least one and preferably an array of primary windings that couple energy inductively to a secondary winding within the device to be recharged. The invention also provides bulky secondary modules that may allow the system to be used with conventional electronic devices.
The requirement for an inductive adaptor, such as Hui's secondary module, for interfacing between inductive outlets and conventional electrical devices, is an inconvenience for the potential users of inductive technology. The need remains, therefore for convenient inductive power receiver integrated into conventional electric devices. Embodiments described below addresses this need.